What is an oligodendroglioma?
Oligodendrogliomas account for 2-5% of all primary brain tumours. They are more common in adults, particularly those aged 40-60.
If you or someone you know has just been diagnosed with an oligodendroglioma, you may be worried about what this means. This is a natural way to feel. Our Support and Information team can help answer any questions you may have or provide a listening ear if you need one.
What is an oligodendroglioma?
Oligodendrogliomas are primary brain tumours that are a type of glioma. They’re the third most-common glioma, accounting for 2-5% of all primary brain tumours and 5-18% of gliomas.
The majority of oligodendrogliomas occur in the frontal lobe, and the second most common site affected is the temporal lobe.
They’re more common in adults, particularly in people aged 40-60, and are slightly more common in men than in women.
Oligodendrogliomas are divided into two types:
- grade two oligodendrogliomas that grow very slowly
- grade three oligodengliomas, also known as anaplastic oligodendroglioma. These grow faster and are more likely to spread. They are more common in older people aged 60-80.
What are the symptoms of an oligodendroglioma?
Oligodendrogliomas may cause any of the symptoms common among brain tumours, particularly:
- altered sensations, like strange smells or hallucinations relating to sense of smell
- muscular weakness, particularly down one side of the body, and loss of control of bodily movements.
Often, the symptoms depend on where the brain tumour is located.
In the frontal lobe, oligodendrogliomas can cause gradual changes in mood and personality, and weakness or numbness in the muscles of one side of the body.
If it is located in the temporal lobe, this may cause problems with speech, coordination and memory.
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How are oligodendrogliomas treated?
As grade 2 oligodendrogliomas grow very slowly, you may be put on active monitoring (also known as watch and wait) if no treatment is required immediately.
If the tumour is large or causing symptoms that affect your quality of life, neurosurgery may be performed to remove as much as possible. This may be followed with radiotherapy or chemotherapy.
Grade 3 oligodendrogliomas are usually treated with surgery soon after diagnosis. This is usually followed by a combination of radiotherapy and chemotherapy because oligodendrogliomas are often ‘diffuse’, which means they’re more difficult to remove completely.
Chemotherapy is particularly successful when it is administered to patients whose tumours contain a particular gene change called the 1p/19q chromosomal deletion. Detecting this genetic alteration with biomarker testing is now essential when evaluating what treatment is used for people who are diagnosed with an oligodendroglioma.
The following biomarker tests have all been shown to be useful in diagnosing and treating ogliodendrogliomas.
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What is the 1p/19q test?
The 1p/19q test may predict long-term survival in people who have oligodendroglioma.
The test can also be useful in diagnosing oligodendrogliomas and, therefore, in making decisions about the most appropriate treatment for you.
How does the test work and what does it show?
Our bodies are made up of cells. Each cell has 23 pairs of chromosomes, which carry your genes (DNA). One chromosome of each pair is inherited from your mother, and the other from your father. Each pair of chromosomes are numbered 1 to 22, then XX or XY.
The 1p/19q test looks at genetic changes to chromosomes 1 and 19 to see whether they have a section missing. If the sections called the p section of chromosome 1 and the q section of chromosome 19 are missing, this means that the genes carried in those sections are also missing.
These genes seem to be involved in resistance to chemotherapy drugs. So if you’re found to be missing both those sections, you’re more likely to have a better response to chemotherapy and longer overall survival.
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What is the IDH1/IDH2 test?
The IDH1/IDH2 test may predict long-term survival in people who have oligodendrogliomas.
It may also be useful in predicting how effective a particular treatment is likely to be.
How does the test work and what does it show?
IDH1 and IDH2 are genes. A change (mutation) in the IDH1/IDH2 genes has been found in about 80% of astrocytomas, oligodendrogliomas and secondary glioblastomas.
Tumours that have the change are known as IDH–mutant, and those without the change are known as IDH-wildtype.
For people with high grade types of these glioma, those whose tumours are IDH-mutant tend to have better long-term survival rates than those who are IDH-wildtype.
It’s not yet clear how mutations of the IDH1/IDH2 genes link to outcomes for people with low grade brain tumours – both in terms of long-term survival and also treatment outcomes. However, there’s some evidence that, similar to high grade gliomas, people whose tumours are IDH-mutant have better long-term survival rates than those who are IDH-wildtype.
Further research needs to be carried out before clear conclusions can be drawn, but it may be that chemoradiotherapy (a combination of chemotherapy and radiotherapy) is more effective for some people with grade 2 gliomas who have the IDH1/IDH2 mutation, than those who don’t. (See TP53/ATRX mutations section further on.)
It’s important to be aware that people with gliomas that have the IDH1/IDH2 mutation tend to be younger adults and older children, which may partially account for their longer survival.
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What is the MGMT methylation test?
For people with anaplastic oligodendroglioma, the MGMT methylation test helps to predict how effective chemotherapy treatment is likely to be, although there are many other factors that also affect response to treatment. This can be used to help plan a suitable, individualised treatment plan.
What does the test show?
In summary, the test looks at the amount (percentage) of something called methylation. If your tumour is found to be:
- MGMT methylated, you’re more likely to respond well to TMZ chemotherapy.
- MGMT unmethylated, you’re less likely to respond to TMZ chemotherapy.
This helps your healthcare team decide on the best course of treatment for you. For example, if your tumour is unmethlyated, giving you high doses of chemotherapy may give you lots of unpleasant side-effects, but with little benefit in terms of reducing your tumour.
If you do decide to have the test, you need to be aware that it may be found to be unmethylated. Speak to your healthcare team about what would happen next if this turned out to be the case.
There are other factors that influence the effectiveness of chemotherapy, so there’ll always be ‘good’ and ‘poor’ responders in both the methylated and unmethylated groups.
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TERT promoter mutation test
When found with 1p/19q co-deletion and IDH-mutant biomarkers, the TERT promoter mutation suggests a diagnosis of oligodendroglioma, and predicts greater benefit from chemotherapy and radiotherapy and longer survival, particularly in grade 2 and 3 gliomas.
However, when the TERT mutation is found on its own in grade 2 and 3 gliomas, it predicts poorer survival. This suggests the need for early, more aggressive treatment.
What treatment do people diagnosed with an oligodendroglioma usually have first?
If you’ve just been diagnosed with an oligodendroglioma and are about to have treatment, you may want to see what other people’s first treatment was. Use the First Treatment insight in BRIAN, which you can personalise to make it relevant to you.
What causes oligodendrogliomas?
As with most tumours, the exact cause is not known, although we do understand some of the risk factors.
This can be a difficult thing to accept and can leave you feeling helpless, but there is nothing you could have done to prevent this from happening.
The Brain Tumour Charity is contributing to the funding of research into a possible cause that is focused around our genes.
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